When To Treat For Grubs in Your Lawn

Grubs, white grubs, grub worms. No matter what you call them, these pests, when left untreated, can wreak havoc in a lawn in absolutely no time. 

Before jumping into prevention, controlling, and killing grubs in your lawn, it’s important to know about the Japanese beetle and its life cycle. 

Grubs are the larval stage of the European chafer, June beetle (June bug) and/or Japanese beetle. These are the most common in New England. Adult Japanese beetles (June bugs) typically lay eggs in lawns in June. The ideal conditions are green healthy, irrigated lawns. As the larvae eggs hatch, they begin to eat the roots of the grass throughout the summer into the early fall months. 

As they eat the roots throughout the summer, you will find irregular patterns of brown patches throughout your lawn, and will be able to peel the grass back like a rug or doot mat. You will find the grubs at the edges of the damaged turf.

As the season winds down and the soil cools, the grubs move deeper into the soil to ‘hibernate’ in a frozen state over winter. And as soil temps begin to rise in the following spring, they’re much larger and begin to slowly feed once again. However, typically spring grubs do not do much (if any) damage to the lawns.

As the season progresses around June, the pupate emerge from the soil as a Japanese beetle, and the egg-laying life cycle process starts all over again.

Since these larger April/May grubs do not pose much threat in the springtime, it is a good sing to begin your preventative treatment. 

Controlling grubs in your lawn

So, how do you prevent grub worms from damaging your lawn? By being prepared. Expect the worst and be prepared with the right products to prevent grub worms at the right time. 

You will want to look for products with the following active ingredients. 

When to treat grub worms in lawn

Sticking with the Northeast and cool season lawns specifically, applying a preventative application of grub control is imperative and timing is everything. These products should be applied in the beginning of June. 

Alway read the labels of the products you’re applying. Generally speaking, these need to be watered in with 1/4″ of water, and will provide preventative grub treatment for 3-4 months. 

Note that Imidacloprid may not last as long as Chlorantraniliprole or Thiamethoxam, and can be applied closer to the middle of June for extended coverage. 

Signs of grub worms in lawn

As previously mentioned, the most telling signs of grubs in your lawn will be irregular dead brown patches of grass (not to be confused with brown patch fungus). This is due to the grub worm larvae munching on the roots of the grass. These patches of grass will be easily peeled back like a carpet, or a blanket. At this point, the grass is dead and will not come back. A full reseed job is in order to restore the lawn.

Below are some images of the aftermath of grub damage.

Not specific to grubs, but an interesting takeaway from Jonathan Green about testing for chinch bugs:

Unusual bird activity on the lawn
Greyish color damage and a contiguous damage pattern.

“The coffee can test” Remove both ends of a large tin can, such as a coffee can.

1. Insert one end of the can into the ground at the very edge of the damage so what is visible in the can is half damaged and half not.
2. Press the can two inches into the soil, leaving about least four inches above the ground.
3. Fill the can with water and wait about five minutes.
3. If chinch bugs are present, they will float to the surface of the water.

How to kill grubs in your lawn

If you missed the window to prevent white grubs and are seeing visible grub worm damage, you need a fast-acting curative. Products with the following active ingredients contain will work quickly.

Some grub worm killers that can be found in big box stores like The Home Depot are:

Summary

Grub worms can do extensive, irreversible damage. If you plan on having a healthy, vigorous green lawn, be sure to stay ahead of these pests by applying preventative chemicals including Imidacloprid, Chlorantraniliprole or Thiamethoxam in early June. And if you or your neighbors have had grub problems in the past, this is a very important step.

If you missed the window and notice active grub damage, use a fast-active grub killer which chemicals include Carbaryl or Trichlorfon (Dylox).

I hope you found this helpful in preventing and treating grub worms in your lawn. Please let me know by commenting below.

Frequently Asked Questions

What are the best products to kill grubs in lawn?

The best products to kill grubs in your lawn contain the active ingredients Carbaryl (Sevin)
or Trichlorfon (Dylox). Products like Jonathan Green Grub & Insect Control contain Imidacloprid & Lambda-Cyhalothrin which can be used to kill grubs, but only in the early larvae stages, but is best used as a preventitive.

What are the best products to prevent grubs in lawn?

The best products to prevent and control grubs in your lawn contain the active ingredients Imidacloprid (Merit, Jonathan Green), Chlorantraniliprole (GrubEx) or Thiamethoxam (Meridian). These products last 3-4 months and should be applied in the beginning of June to help prevent grub worms.

How do grubs damage your lawn?

Grubs are the larvae of the Japanese beetle (June bug). As the larvae hatch, they begin to eat the roots of your grass – not the grass blades themselves (those are chinch bugs). As the grubs finish eating the roots, they move outwards to more roots. This causes the irregular dead brown patches of grass.

What are grub worms?

Grubs are most commonly the larval stage of the European chafer, June beetle (June bug) and Japanese beetle. Adult beetles lay their eggs in the early summer in June and July; larvae hatch and begin to eat the grass roots throughout the summer and into early fall; grubs reemerge in the spring overwinter, pupate in late May and into June, and the lifecycle begins all over again.

References:
https://ag.umass.edu/turf/fact-sheets/current-insecticide-approaches-for-white-grub-control

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